Pixel 4 Face Unlock Doesn't Care If You're Sleeping

Google's Face Unlock on the new Pixel 4 may make accessing the new Android smartphone more straightforward, but it could also make it easier for others to unlock the device when you're sleeping. The latest in the Pixel series does away with the fingerprint sensor on the last-generation Pixel 3, instead recognizing faces for what Google has said will be faster and more secure.

Certainly, it's a speedy system. Whereas the Pixel 3 required users to tap their finger against the circular scanner on the back of the phone, the Pixel 4 can be set to automatically wake when you lift it, and – assuming your face is recognized – be unlocked by the time you're looking at the display.

Unfortunately, that doesn't take into account whether it's you doing the lifting or someone else – say, while you're taking a nap. The Pixel 4 will recognize faces whether the user has their eyes open or not. A warning in the Face Unlock settings screen cautions that there may be unintended security consequences as a result of that.

"Looking at the phone can unlock it when you don't intend to," Google's notes point out. "Your phone can be unlocked by someone else if it's held up to your face, even if your eyes are closed. Your phone can be unlocked by someone who looks a lot like you, say, an identical sibling."

A spokesperson for Google confirmed to the BBC that, when the Pixel 4 and Pixel 4 XL ship to preorder customers later this month, the functionality will still operate as it does on initial units provided to reviewers.

Of course, it's not like the fingerprint sensor on Google's older Pixel phones – or indeed those from any other manufacturer – would differentiate between the finger of someone awake and intentionally unlocking their device, or asleep and having someone else do so. Nonetheless, Google's Face Unlock behavior is at odds with how Face ID on Apple's iPhones operates.

With Face ID, one of the criteria for unlocking the iPhone is that the user's eyes be open. Without that, iOS will remain secured, and can even mask the content of notifications shown on the lock screen. Apple does offer a setting to "require attention for Face ID," which controls whether active attention to the phone is necessary.

Android, however, doesn't offer such a setting, even though leaks in advance of the Pixel 4's release suggested earlier versions might have a control to prevent Face Unlock from working if someone had their eyes closed. "We will continue to improve Face Unlock over time," a Google spokesperson told the BBC.

Biometric security and the legal rules surrounding whether police and security forces can compel people to unlock their devices with fingerprints or facial recognition has become a hot topic in recent years, as smartphones shift away from relying on PIN security alone. Forcing someone to reveal their PIN or password has long been prevented by the Fifth Amendment in the US, but biometric security was a gray area. Earlier this year, however, the District Court for the Northern District of California ruled that being forced to unlock with face and fingerprint security would count, under the Fifth Amendment, as self-incrimination.

That's yet to be tested in higher courts, mind, and the general advice is that, for those who are particularly concerned about others accessing their smartphones and other devices, a strong PIN or passcode should still be used instead.

Google does have a "Lockdown" feature for Android, which can temporarily switch off Face Unlock – or other biometric security, phone depending – as well as preventing notifications. In order to be accessed it must first be enabled in the Android settings. After that, holding down the power button will show a "Lockdown" option in the menu; to turn it off, the phone's PIN must be entered.